This invention relates to the recovery of gasoline vapors from gasoline dispenser systems.
As smog conditions have gone from bad to worse in large cities, every effort has been made to reduce the amount of hydrocarbons released into the atmosphere from all sources. One relatively large source of atmospheric hydro-carbons is gasoline vapors expelled from the gasoline tanks of automoblies when they are being refueled. Before being refueled, the nearly empty gasoline tank is filled with gasoline vapor. As gasoline is being pumped into the empty tank, the gasoline vapor is pushed out of the tank and into the atmosphere through the clearance between the refueling nozzle and the gasoline inlet opening. Gasoline vapor released into the atmosphere in this manner amounts to 15% of the total hydro-carbons released from the tailpipes of automobiles. Therefore in recent years, efforts have been made to develop vapor recovery systems for preventing the gasoline vapors from being released into the atmopshere during refueling.
Basically, these systems involve creating a vapor seal over the gasoline inlet opening when the refueling nozzle is inserted therein and providing a vapor recovery conduit which extends from the nozzle to the underground gasoline storage tank so that the gasoline vapors are pushed or drawn into the storage tank during the refueling instead of being released into the atmosphere.
There are two different types of vapor recovery systems: The balanced system and the vacuum-assist system. The balanced system relies on the push exerted on the gasoline entering the gasoline tank and displacing the gasoline vapor which had previously filled the tank. This push is sufficient to move the vapors down the vapor recovery conduit into the underground gasoline storage tank. Since the volume of vapor displaced by gasoline entering the gasoline tank is equal to the volume left vacant by gasoline leaving the storage tank, there is always room in the storage tank for the displaced vapor.
The vacuum-assist system uses a vacuum or other assist means to draw the gasoline vapor into the underground storage tank. The balanced system requires a relatively tight vapor seal at the gasoline inlet opening to prevent any vapor from escaping into the atmosphere. Since a tight vapor seal is difficult to obtain on some cars, the balanced system is not as efficient as the vacuum-assist system. There are many small stations, however, where the efficiency of a vacuum-assist system is not required.
In both the balanced system and the vacuum-assist system, a valve is placed on the gasoline vapor line and means are provided for opening the valve when the gasoline is being dispensed and closing it when gasoline is not being dispensed so that the gasoline vapor recovery line is only open when gasoline is being dispensed. In some systems, the valve is operated by a switch which works on the dispenser switch. In other words, when the dispenser is turned on, the valve is turned on, and when the dispenser is turned off, the valve is turned off. In other systems, a flow sensor is placed somewhere in the gasoline line and to create a differential pressure which indicates the flow of gasoline through the line. This differential pressure is used to turn the valve off and on.
This invention relates to gasoline recovery systems of either the balanced type or the vacuum-assist type which utilizes a flow sensor for opening and closing the valve in the gasoline vapor line. One prior art system of this type is disclosed in U.S. Pat. No. 4,057,085 issued on Nov. 8, 1977 to Marwan S. Shihabi. This systen has the flow sensor and the pressure responsive valve formed in a common housing which also houses the conduits which connect the pressure responsive valve to the flow sensor. This housing is mounted on the gasoline dispenser and is connected to the gasoline storage tank through conduits which require impact valves at their lower portion as a safety measure. The impact valves turn off in response to the impact of a car crashing into the dispenser to cut off the flow of gas and to close the gasoline vapor recovery line.